It's just a fancy number to dupe consumers who don't know any better into spending more money. 4GB must be better than 2GB, right?

Now, what they could do is launch Crossfire/SLI on a stick for each core. Have a twin-7850, twin-7870, twin-7950 card, etc, all at different price points, with efficient coolers, and slightly cheaper than buying 2x the respective cards.